Period	Percent
1970-01-01	15.90
1975-01-01	20.34
1980-01-01	24.90
1985-01-01	19.33
1990-01-01	21.38
1995-01-01	24.03
2000-01-01	26.93
2005-01-01	44.05
2010-01-01	47.67